const obj = {
  0: "1801A",
  1: '高级程序设计',
  2: '数据结构',
  3: '数组',
  length: 4,
  [Symbol.iterator]: Array.prototype[Symbol.iterator]
}

// for(let i = 0; i < length; i++) {} // 数组 字符串 对象X
// for(let val in obj) {}
// while() {}

// for (let i = 0; i < obj.length; i++) {
//   console.log(obj[i])
// }
// forEach map filter reduce some every
// for (let key in obj) {
//   console.log(obj[key])
// }

// 遍历器：前器：凡是具有遍历器接口的东西，我都能遍历
// Symbol.iterator

const arr = ['devin', 'wyp', '1801A', 'javascript']
// const obj = {}  obj is not iterable
for (let key of obj) {
  console.log(key)
  // console.log(arr)
}


// require('open')('http://localhost:7001')
